FIG. 8 is a top view of conventional acoustic wave resonator 1 disclosed in Japanese Patent Unexamined Publication No. 2008-78981. Acoustic wave resonator 1 includes: piezoelectric substrate 2; busbar 3 provided on piezoelectric substrate 2; busbar 4 provided on piezoelectric substrate 2 to be parallel to busbar 3; electrode fingers 5 provided on piezoelectric substrate 2; and electrode fingers 6 provided on piezoelectric substrate 2. Electrode fingers 5 have respective one ends connected to busbar 3, and extend to busbar 4. Electrode fingers 6 have respective one ends connected to busbar 4, and extend to busbar 3 to interdigitate with electrode fingers 5. Busbars 3 and 4 extend in direction D11. Electrode fingers 5 and 6 extend in direction D12 perpendicular to direction D11.
FIG. 9 is a propagation characteristic chart of acoustic wave resonator 1. In FIG. 9, the horizontal axis represents a frequency, the left vertical axis represents attenuation, and the right vertical axis represents the attenuation at an enlarged scale. FIG. 9 shows propagation profiles 7 and 7E of acoustic wave resonator 1. The scale of the left vertical axis is applied to propagation profile 7. The enlarged scale of the right axis is applied to propagation profile 7E. Propagation profiles 7 and 7E of acoustic wave resonator 1 exhibit spurious response S11 caused by a transverse mode in the vicinity of a resonance frequency. Spurious response S11 causes the deterioration and decline of a Q value of acoustic wave resonator 1.